U.S. patent number 5,551,650 [Application Number 08/260,945] was granted by the patent office on 1996-09-03 for active mounts for aircraft engines.
This patent grant is currently assigned to Lord Corporation. Invention is credited to Douglas E. Ivers, Steve C. Southward.
United States Patent |
5,551,650 |
Southward , et al. |
September 3, 1996 |
Active mounts for aircraft engines
Abstract
An active mount for fixed wing applications. One aspect of the
invention provides decoupling of two tones which are close in
frequency by positioning the mount actuators and error sensors in
the primary transmission path of the disturbance vibration and by
providing adequate spatial separation between the two sets of error
sensors to reduce or eliminate cross-coupling of the signals.
Another aspect of the invention utilizes orthogonally positioned
actuators with corresponding actuators of paired mounts being
focalized for each engine.
Inventors: |
Southward; Steve C. (Cary,
NC), Ivers; Douglas E. (Cary, NC) |
Assignee: |
Lord Corporation (Erie,
PA)
|
Family
ID: |
22991302 |
Appl.
No.: |
08/260,945 |
Filed: |
June 16, 1994 |
Current U.S.
Class: |
244/54;
267/140.15; 244/17.27; 244/1N |
Current CPC
Class: |
F16F
13/08 (20130101); F16F 15/00 (20130101); G10K
11/17883 (20180101); G10K 11/17857 (20180101); F16F
15/08 (20130101); F16F 1/40 (20130101); F16F
7/1005 (20130101); F16F 15/027 (20130101); G10K
2210/321 (20130101); G10K 2210/121 (20130101); G10K
2210/129 (20130101); G10K 2210/1281 (20130101); G10K
2210/123 (20130101); G10K 2210/3016 (20130101); G10K
2210/107 (20130101) |
Current International
Class: |
F16F
15/023 (20060101); G10K 11/00 (20060101); F16F
15/027 (20060101); F16F 15/00 (20060101); F16F
7/10 (20060101); G10K 11/178 (20060101); B64D
027/00 () |
Field of
Search: |
;244/54,17.27,1N
;267/140.14,140.15 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0621418A2 |
|
Aug 1993 |
|
EP |
|
2132053 |
|
Dec 1982 |
|
GB |
|
Other References
Lyubashevskii et al., Adaptive Cancellation of the Discrete
Components of Noise, 1992 May-Jun..
|
Primary Examiner: Kashnikow; Andres
Assistant Examiner: Dinh; Tien
Attorney, Agent or Firm: Thomson; Richard K. Wayland;
Randall S. Wright; James W.
Claims
What is claimed is:
1. A system for minimizing vibration transmitted from a plurality
of power plants, including a first power plant operating at a
frequency N.sub.1R and a second power plant operating at a
frequency N.sub.1L, where N.sub.1R and N.sub.1L are equal or nearly
equal, into a passenger compartment of an aircraft, said system
comprising
a) a first active mount securing a first of said power plants to a
first portion of an aircraft structure, said first active mount
including first actuator means;
b) a second active mount securing a second of said power plants to
a second portion of said aircraft structure, said second active
mount including second actuator means;
c) first sensor means mounted proximate said first power plant for
detecting vibration induced by said first power plant and for
producing a first signal representative thereof, said first sensor
means being spaced sufficiently far away from said second power
plant to minimize an influence of N.sub.1L on said first
signal;
d) second sensor means mounted proximate s aid second power plant
for detecting vibration induced by said second power plant and for
producing a second signal representative thereof, said second
sensor means being spaced sufficiently far away from said first
power plant to minimize an influence of N.sub.1R on said second
signal;
e) signal processing means for converting said first and second
representative signals into first and second control signals for
said first and second actuator means of said first and second
active mounts, respectively;
whereby said first and second sensor means are positioned so as to
decouple the response of said actuators to their respective first
and second representative signals.
2. The system for minimizing vibration of claim 1 wherein said
first and second portions of said aircraft structure to which said
power plants are secured are positioned on opposite sides of said
passenger compartment.
3. The system for minimizing vibration of claim 1 wherein said
first and second sensor means each comprise a tachometer providing
first and second input signals representative of N.sub.1R and
N.sub.1L, respectively, and error sensor means representative of a
level of vibration transmitted through said mount.
4. The system for minimizing vibration of claim 3 wherein said
first and second error sensor means are positioned on the structure
side of said mounts for said first and second power plants,
respectively.
5. The system for minimizing vibration of claim 4 wherein said
error sensor means are mounted in a primary disturbance path
between said power plant and said support structure for its
respective power plant.
6. The system for minimizing vibration of claim 5 wherein said
first and second sensor means are capable of sensing frequency,
phase and amplitude of said vibrations.
7. The system for minimizing vibration of claim 3 comprising a
tonal control system in which said first tachometer detects a first
operating frequency N.sub.1R of said first power plant and produces
a signal representative of N.sub.1R and said second tachometer
detects a second operating frequency N.sub.1L of said second power
plant and produces a signal representative of N.sub.1L.
8. The system for minimizing vibration of claim 7 wherein said
first and second control signals are phase shifted signals whose
amplitude has been modified which are also representative of
N.sub.1R and N.sub.1L input to said first and second actuator
means, respectively, to cancel the vibrational effects of N.sub.1R
and N.sub.1L.
9. The system for minimizing vibration of claim 8 wherein said
actuator means comprises first and second orthogonal force
transmission elements which are mounted such that each may deliver
a force having a horizontal and a vertical component.
10. The system for minimizing vibration of claim 3 wherein said
first and second power plants each produce a secondary disturbance
tone N'.sub.1R and N'.sub.1L, respectively, and said system
includes means to minimize transmission of vibration resulting from
these secondary disturbance tones including third and fourth input
signals provided by a tachometer.
11. A system for minimizing vibration transmitted from a plurality
of power plants, including a first power plant operating at a
frequency N.sub.1R and a second power plant operating at a
frequency N.sub.1L, where N.sub.1R and N.sub.1L are equal or nearly
equal, into a passenger compartment of an aircraft, said system
comprising
a) a first sync signal generating means for producing a signal
representative of disturbance signal N.sub.1R ;
b) a second sync signal generating means for producing a signal
representative of disturbance signal N.sub.1L ;
c) first error sensor means mounted proximate said first power
plant on a structural support for detecting vibration induced by
said first power plant in said support and for producing a first
signal representative thereof, said first error sensor means being
spaced a sufficient distance from said second power plant so that
the influence of N.sub.1L on said first signal is minimal;
d) second error sensor means mounted proximate said second power
plant on a structural support for detecting vibration induced by
said second power plant in said support and for producing a second
signal representative thereof, said second error sensor means being
spaced a sufficient distance from said first power plant so that
the influence of N.sub.1R on said second signal is minimal;
e) a first output device for producing a counter-phased vibration
to minimize the transmission of N.sub.1R to its respective support
structure;
f) a second output device for producing a counter-phased vibration
to minimize the transmission of N.sub.1L to its respective support
structure;
g) signal processing means for receiving said first and second sync
signals and said first and second representative signals and
producing first and second control signals for said first and
second output devices, respectively;
whereby said first and second error sensor means are positioned so
as to decouple the response of said output devices to their
respective first and second representative signals.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to the area of active vibration control.
Specifically, the invention relates to improvements in active
mounts for fixed wing applications. More specifically, this
invention is directed to a system for cancelling two tones which
are relatively close in frequency, as in the case of the primary
(and/or secondary) disturbance frequencies of pairs of turbofan or
turboprop engines.
In the realm of active noise and vibration control, there are three
implementation approaches: active noise control, which uses an
inverse-phase sound wave to cancel the disturbance signal; active
structural control, which vibrates a structural component at a
frequency to cancel the input disturbance (noise and/or vibration);
and active isolation control, where an actuator in a mount is
reciprocated at the proper frequency, phase and amplitude to cancel
the input disturbance (which, again, may be a structural vibration
or in the audible range, in which case it is experienced as noise).
The decoupling feature of the present invention can be utilized
with each of these three implementation approaches.
Active mounts for controlling vibrational input from an engine to
the support structure are known. For example, commonly assigned
U.S. Pat. No. 5,174,522 issued to Hodgson teaches the use of an
active fluid mount for vibration cancellation. Systems which
actively control vibration or sound by using an out of phase
cancellation signal are also known and include U.S. Pat. Nos.
4,677,676 to Eriksson, 4,153,815 to Chaplin, 4,122,303 to Chaplin
et al., 4,232,381 to Rennick et al., 4,083,433 to Geohegan, Jr. et
al., 4,878,188 to Zeigler, Jr., 4,562,589 to Warnaka et al.,
4,473,906 to Warnaka et al., 5,170,433 to Elliott, 4,689,821 to
Salikudden et al., and 5,133,527 to Chen et al. These systems
utilize digital microprocessors (processors) to control or minimize
mechanical vibration or ambient noise levels at a defined location
or locations, as for example noise or vibration experienced in an
aircraft cabin or within an automobile passenger compartment.
Generally, these systems are responsive to at least one external
input signal such as a synchronizing tachometer signal and/or error
signal as supplied by various types of sensors such as microphones,
accelerometers, etc. These systems strive to reduce to zero, or at
least minimize, the recurring sound and/or vibration.
Multiple-input, multiple-output (MIMO) systems are required to
adequately compensate for the vibrations of plural turbofan or
turboprop engines. In active control systems of the above-mentioned
type, it is generally required to have an input signal for each
tone to be canceled which is supplied to an adaptive filter and/or
a processor which is indicative of the frequency content and/or
amplitude/phase of the input source, i.e., indicative of the
disturbance signal. Particularly, it is usually required to have
two or more analog or digital waveforms, such as a sine and cosine
wave, that are synchronized with (at the same frequency as) the
input source signal for providing the appropriate information to
the processor and/or adaptive filter. These waveforms will be
utilized in computing the appropriate frequency and amplitude of a
cancellation signal in accordance with a particular algorithm such
as least mean square (LMS) and filtered-x LMS algorithms.
Many such algorithms have difficulty processing two tones which are
close in frequency such as in the case of a right engine operating
at a first frequency N.sub.1R and a left engine operating at a
second frequency N.sub.1L which is the same or nearly the same as
the first frequency. Turbofan and turboprop engines typically have
four tones that are objectionable: N.sub.1R which corresponds to
the frequency of the right fan or prop, N'.sub.1L which corresponds
to the frequency of the right turbine, N.sub.1L which corresponds
to the left engine fan or prop and N'.sub.1L which corresponds to
the left engine turbine frequency. These similar tones (N.sub.1R
and N.sub.1L or N'.sub.1R and N'.sub.1L) can cyclicly reinforce one
another creating a particularly objectionable beat frequency. The
relative closeness of the two tones can cause the system to become
unstable as the algorithm seeks to find an optimal cancellation
solution.
In practice, each of the error sensors of such a system will pick
up all four of the engine disturbance frequencies, to some degree.
The most general controller objective is for each actuator to
provide a cancellation force at each of the four tones. The
controller would provide a signal segment of sufficient amplitude
and phase inverted to cancel each of the individual four
components, then superpose the four signal segments into a single
cancellation signal (complex sine wave) to be fed to the actuator.
When any two of the four tones are relatively close in frequency
(and generally there are two pairs of such tones), the control
algorithm can have difficulty converging to a stable set of
actuator signals.
The present invention provides decoupling of the response to the
two tones having similar/identical frequencies by proper
positioning of the sensors and the actuators. Preferably, both the
sensors and actuators can be placed in the primary disturbance path
between the power plant (or engine) and the support structure. (In
the case of active isolation control, the actuator will necessarily
be in the primary disturbance path. In the case of active noise
cancellation, the microphones will not be in the primary
disturbance path.) In addition, the error sensors must be widely
spaced enough to prevent cross-coupling of the closely spaced
frequencies (N.sub.1R and N.sub.1L, for example). By spatially
separating the error sensors, the magnitude of the signal N.sub.1L
detected by the sensors positioned to monitor the N.sub.1R signal
and visa versa, will be small enough that it can be ignored (i.e.,
will be at least an order of magnitude smaller) or may be filtered
out by the signal conditioner.
In another aspect of the invention, pairs of sets of force
transmission elements within the active mount are positioned such
that each element can transmit a vertical force component and a
horizontal force component. Further, one of the force transmission
elements from each of the mounts is targeted to focalize its
cancellation force (i.e., the elastic center, the point at which
the axes of force intersect, is at or beyond the center of gravity
of the power plant). Focalization is well known in the mounting
art, and is more particularly described in U.S. Pat. Nos. 2,175,999
issued to Taylor and 2,241,408 issued to Lord which are hereby
incorporated by reference. Preferably, the two force transmission
elements are orthogonally oriented. Further, in one embodiment,
each transmission element is preferably oriented at a 45.degree.
angle to the horizontal. In a second alternative embodiment, the
orthogonal actuators may be arranged to act along horizontal and
vertical axes, respectively. The actuators may be tuned absorbers,
electromagnetic, electrohydraulic or piezoelectric.
Various other features, advantages and characteristics of the
present invention will become apparent after a reading of the
following specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic depiction of the electrical interconnection
of the various system components;
FIG. 2 is a cross-sectional end view of one embodiment of active
mount useful in the cancellation system of the present invention;
and
FIG. 3 is a cross-sectional end view of a second embodiment of
active mount useful in the cancellation system of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The cancellation system of the present invention is depicted in
FIG. 1 generally at 10. While the invention is shown in FIG. 1
implemented with an active isolation control system, it will be
appreciated that the invention may also be used in active
structural control and active noise control systems, as well. The
active isolation control system may utilize a waveform generator of
the type described in commonly assigned U.S. patent application
Ser. No. 08/245,719 filed May 18, 1994 entitled "Waveform
Generator" to produce the sync signals S.sub.1, S.sub.2, S.sub.3,
and S.sub.4, which application is hereby incorporated by reference.
Further, the system may utilize as its digital signal processing
controller 20 the feedforward control processor of U.S. patent
application Ser. No. 08/245,717 filed May 18, 1994, which
application is hereby incorporated by reference. Engine support
beam 11 extends through a portion of the fuselage of a fixed-wing
aircraft (not shown) and interconnects first (13) and second (15)
crescent-shaped support arms. At the extremities of support arms
13, 15 are pairs of active mounts 12 and 14. Active mounts 12
support right engine 17 and active mounts 14 support left engine
19. Each mount includes a pair of actuators or force transmission
elements 16 orthogonally positioned between the engine and the
airframe or exclusively positioned on the structural support side
of the mount (FIG. 3) and two or more sensors 18 on the structure
side of the mount. Active mounts 12, 14 may be either the front or
rear mounts of the engine with a more conventional passive mount
being utilized at the alternate location.
At least one reference signal is needed, with two sync signals
S.sub.1, S.sub.2 being shown. These sync signals are transmitted
from the right engine 17 to controller 20 and two sync signals
S.sub.3, S.sub.4 from left engine 19. Signals S.sub.1, S.sub.2 are
representative of the frequency, and phase of N.sub.1R and N.sub.2R
of the right engine 17, while S.sub.3, S.sub.4 are representative
of the frequency and phase of N.sub.1L and N.sub.2L of left engine
19. These sync signals may be provided by a tachometer,
accelerometer, magnetic pickup or other sensor associated with the
shaft of the turbine, or the like as indicated in FIG. 1 at 18'. It
will be remembered that when the term "tachometer" is used herein,
it is used representatively of other similar sensors. Adaptive
filters within controller 20 provide weighting factors which are
computed in accordance with a preferred algorithm (usually LMS or
filtered-x LMS) and phase timing to controller signals 21 which are
fed to force transmission elements 16 upper and lower mounts 14
through amplifiers 28 to cancel or minimize transmission of the
N.sub.1R, N.sub.2R, N.sub.1L and N.sub.2L vibration tones. Sensors
18 feedback the error signals 23 to the controller 20 through
signal conditioner 22 to initiate correction to the calculations of
the amplitude computed by the algorithm as well as the phase shift
to effect minimization.
As mentioned earlier, the normal control theory involves each error
sensor 18 detecting some amount of each objectionable tone and each
actuator 16 receiving a controller signal 21 which attempts to
fully cancel the tones received. If any two of the disturbance
tones are close in frequency, many algorithms are unable to produce
a stable control signal for cancellation. The present solution
proposes positioning both the actuators 16 and the error sensors 18
in the primary disturbance path between the engines 17, 19 and the
support structure 13, 15. Further, the sensors of right engine
mounts 12 must be adequately separated from left engine mounts 14
that cross coupling of the tones does not occur (i.e., the
component of the right engine tones N.sub.1R and N'.sub.1R received
at the left engine mount 14 will be at least an order of magnitude
smaller than those received from the left engine 19 and can be
disregarded). By this positioning, the system achieves both tonal
decoupling (i.e., the left side actuators of mounts 14 will only
attempt to control the tones N.sub.1L and N'.sub.1L, while the
actuators of the right mounts 12 will only attempt to control the
N.sub.1R and N'.sub.1R tones), and sensor decoupling (sensors of
right engine mounts 12 will only stimulate actuators of right
engine mounts 12, while the sensors of left engine mounts 14 will
stimulate actuators 16 of left engine mounts 14). This decoupling
of the response to tones which are relatively close in frequency
(such as N.sub.1R and N.sub.1L as well as N'.sub.1R and N'.sub.1L)
overcomes the stability problems which occur with algorithms such
as LMS and filtered-x LMS.
The force transmission elements (actuators) 16 are orthogonally
positioned and may each form a 45.degree. angle with the horizontal
as depicted in FIG. 1. This has some advantages in that each
actuator 16 is able to deliver equal amounts of vertical and
horizontal cancelling vibrations. In an alternative embodiment, one
actuator may be positioned to deliver force radially and the second
tangentially with respect to the engine. In yet a third embodiment,
actuators 16 may be positioned such that the first extends along a
horizontal axis and the second along a vertical axis (the upper
mounts 12, 14 would have actuators extending downwardly with the
lower mounts having actuators extending upwardly). In any event, it
is desired that the lines of force along which two of the actuators
16 operate be focalized. That is, that the lines of force intersect
at the center of gravity of their respective engine or beyond (as
measured from the actuators). By focalizing the mounts, the mounts
can be made soft tangentially, and comparatively rigid radially,
and still support the engine. Since the mount is soft tangentially,
little if any force will be transmitted in the tangential direction
and the number of actuators required for tangential force
cancellation can be significantly reduced and, in some cases,
tangential actuators can be eliminated.
The active mounts 12, 14 may be of the type described in FIG. 9 of
U.S. patent application Ser. No. 08/145,430 filed Oct. 29, 1993,
which is hereby incorporated by reference. As seen in FIG. 2, mount
12 (which is equivalent of mount 14) has four orthogonally
positioned actuators 16. Four actuators are required for those
actuator types which only have capacity for force in one direction.
For other actuators, only two units are needed as shown in FIG. 3.
Center frame 24 surrounds pylon 25 while outer frame 26 houses the
mount. One of the pylon 25 and outer frame 26 are attached to
supports 13, 15 while the other is attached to its respective
engine 17, 19. Generally, center frame 24 will be connected to the
supports and the outer frame to the engines 17, 19. However, FIGS.
2 and 3 show the center frame connected to the engine and the outer
frame 26 to the supports 13, 15. Error sensors 18 may be positioned
anywhere on the airframe side of the mount and are shown here
attached to the exterior of center frame 24. The FIG. 2 embodiment
depicts the actuators as electrohydraulic; however, they may
alternatively be electromagnetic or piezoelectric or replaced by a
speaker without departing from the invention.
FIG. 3 depicts yet another embodiment of mount 14 in which the
actuators take the form of tuned absorbers 16'. The absorber are
shown here on the engine side mounted on center frame 24. These
orthogonal, focalized absorbers reduce vibration transmitted across
mount 14 to the outer frame 26 and, hence to the supports 13, 15.
These active absorbers 16' can be vibrated at any frequency but are
tuned to deliver the most force at one particular frequency,
usually N.sub.1R and N.sub.1L.
By the present invention, the response to two tones which are
relatively close in frequency are decoupled enabling the controller
to compute and transmit cancellation signals which will effectively
minimize the transmission of these signals, be they structural
vibration or audible tones experienced as noise. While these
embodiments have been described in terms of an active mount, the
decoupling features of the present invention are equally applicable
to active structural control and active noise control systems as
well. In this regard, the actuators may be replaced by other output
devices such as speakers for active noise control applications.
Another feature of the present invention is the orthogonal
positioning of the actuators within the mount with the focalization
of the lines of force in order to reduce the number of tangential
actuators required.
Various modifications, alternatives and changes will become
apparent to one of ordinary skill in the art following a reading of
the foregoing specification. It is intended that all such
modifications, alternatives and changes as fall within the scope of
the appended claims be considered part of the present
invention.
* * * * *